Cobalt-ruthenium catalysts for Fischer-Tropsch synthesis

ABSTRACT

A hydrogen regenerable hydrocarbon synthesis catalyst useful for preparing higher hydrocarbons from synthesis gas is prepared by depositing cobalt and ruthenium on a refractory carrier and oxidizing and reducing the catalytic metals to form a catalyst in which the cobalt and ruthenium are in intimate contact.

This is a division of application Ser. No. 881,347, filed July 2, 1986,now U.S. Pat. No. 4,738,948.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved catalyst for producinghydrocarbons from synthesis gas, hydrogen and carbon monoxide, and toimprovements in the hydrocarbon synthesis process. Specifically, thisinvention relates to a catalyst comprising cobalt and ruthenium incatalytically active amounts on a titania support and a process forutilizing the catalyst that allows on-stream regeneration and cyclicaloperation without having to remove the catalyst from the hydrocarbonsynthesis reactor.

2. The Prior Art

Methane is available in large quantities in many areas of the world.Some methane is generated from refinery applications while large amountsof methane, as the principal constituent of natural gas, are found indeposits in various areas. Methane can be used as a gas, for example,for heating purposes, and can be transported by pipeline or as aliquefied gas over long distances. Where use of the methane as a gas isnot economic or the transportation of methane requires traversingoceans, the methane can be converted to a liquid which is more easilytransported and may have significantly higher value than methane gas.

Conversion of methane is normally carried out in a two-step procedureinvolving reforming the methane to produce hydrogen and carbon monoxide,synthesis gas, and converting the synthesis gas to higher hydrocarbons,C₅ +, in a Fischer-Tropsch type reaction. Both steps of the process arewell known and can be readily illustrated: the first step by U.S. Pat.Nos. 1,711,036, 1,960,912 and 3,138,438; the second step by U.S. Pat.Nos. 4,477,595, 4,542,122, and 4,088,671.

This invention is concerned with the second step, the well knownFischer-Tropsch type reaction which will be referred to hereinafter ashydrocarbon synthesis.

This invention is primarily concerned with cobalt and rutheniumcatalysts for hydrocarbon synthesis and both of these metals have beendisclosed as being useful in such reactions, either alone, jointly, orwith other materials. What has not been disclosed in the art is thecombination of steps required to produce a composition that is novel andhas superior catalytic properties to other cobalt, ruthenium, orcobalt-ruthenium catalysts. These properties include: improved COconversion, improved volumetric productivity, enhanced selectivity toC₅ + and lower CH₄ and the ability to regenerate the catalyst atrelatively low temperatures without removing it from the reactor.

U.S. Pat. No. 4,477,595 discloses ruthenium on titania as a hydrocarbonsynthesis catalyst for the production of C₅ to C₄₀ hydrocarbons with amajority of paraffins in the C₅ to C₂₀ range. U.S. Pat. No. 4,542,122discloses a cobalt or cobalt-thoria on titania having a preferred ratioof rutile to anatase, as a hydrocarbon synthesis catalyst. U.S. Pat. No.4,088,671 discloses a cobalt-ruthenium catalyst where the support can betitania but preferably is alumina for economic reasons. U.S. Pat. No.4,413,064 discloses an alumina supported catalyst having cobalt,ruthenium and a Group IIIA or Group IVB metal oxide, e.g., thoria.European Patent 142,887 discloses a silica supported cobalt catalysttogether with zirconium, titanium, ruthenium and/or chromium.

SUMMARY OF THE INVENTION

The invention resides in the preparation of a novel catalyst and the useof that catalyst in hydrocarbon synthesis reactions. The catalyst iscomprised of cobalt and ruthenium, in intimate association, deposited ona titania support. Evidence suggests that atoms of cobalt and rutheniumare present in the same crystallite and that this intimate associationof the metals provides the advantages mentioned hereinbelow.

The catalyst, when prepared as described herein, is an excellenthydrocarbon synthesis catalyst and may be used in hydrocarbon synthesisreactions as other known catalysts are used, for example, as pelletsloaded in tubes through which synthesis gas is passed and converted intohigher hydrocarbons. The advantages of employing the particularcobalt-ruthenium catalyst of this invention in hydrocarbon synthesisare: lower methane yields and increased C₅ + yields relative to a cobaltcatalyst or a cobalt-ruthenium catalyst that has not been oxidized andre-reduced in accordance with this disclosure, greater cobalt timeyields (that is, greater conversion of CO and H₂ per gram atom of cobaltper unit of time--a measure of catalyst activity) and the ability toregenerate the catalyst, in situ, under low temperature flowinghydrogen. The last advantage differentiates from carbon burningoperations which must take place at relatively high temperatures, e.g.,400° C. or higher in oxygen and, generally, requires removal of thecatalyst from the reactor, an expensive, time-consuming operation incommercial reactors.

Ruthenium may promote hydrogenolysis and the intimate association ofruthenium with cobalt might allow carbon deposits on the catalyst to begasified via hydrogenolysis as opposed to carbon gasification viacombustion with oxygen in cobalt catalysts other than those having thestructure disclosed herein.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect of intimate association of cobalt and rutheniumon reduction temperatutres as opposed to cobalt alone. The TG curvemonitor's weight changes as the supported cobalt oxide is reduced inhydrogen from room temperature to 500° C. at 6 deg/min. The DTG plotsthe rate of weight change with time as a function of temperature. FIG. 1shows that the onset of reduction begins at a lower temperature with acalcined cobalt-ruthenium catalyst. A cobalt-ruthenium catalyst notprepared in accordance with the procedures of this invention and whereinthe cobalt and ruthenium are not intimately associated, reacts similarlyas a cobalt only catalyst.

FIG. 2 shows the effect of cobalt and ruthenium being in intimatecontact on catalyst carburization, i.e., the tendency of carbon to growon active sites of the catalyst as opposed to a cobalt only catalyst.FIG. 2 follows the behavior of the catalysts heated from roomtemperature to 500° C. in 1:1 H₂ /CO following a prereduction. The largegain of weight between 300° and 500° C. results from the growth ofcarbon. When the cobalt and ruthenium are in intimate contact, thegrowth of carbon is suppressed.

The cobalt only catalyst behaves similarly to a cobalt-rutheniumcatalyst wherein the cobalt and ruthenium are not in intimate contact,i.e., not precalcined.

FIG. 3 and 4 show the results of traces of a cobalt-ruthenium catalystprepared in accordance with this invention and developed from analysiswith a high resolution transmission electron microscope with scanningtransmission and energy dispersive x-ray analysis capabilities. FIGS. 3and 4 show energy dispersive x-ray traces (EDX) of calcined anduncalcined CoRu/TiO₂ catalysts. The figures show that following thecalcination and rereduction treatment the ruthenium has concentrated inthe area of the cobalt particle rather than remaining uniformly presentthroughout the support as it appears on the uncalcined, reducedcatalyst.

DETAILED DESCRIPTION

In general, the hydrocarbon synthesis reaction is carried out atconditions that are known in the art. The H₂ :CO ratio is at least about0.5 and up to about 10, preferably 0.5 to 0.4, and more preferably about1.0 to 2.5. The gas hourly space velocity can range from about 100v/hr/v to about 5000 v/hr/v, preferably from about 300 v/hr/v to about1500 v/hr/v and reaction temperatures may range from about 160° C. toabout 300° C., preferably about 190° C. to 260° C., while pressures areabove about 80 psig, preferably about 80 to 600 psig, more preferablyabout 140 to 400 psig. Hydrocarbon synthesis results in the formation ofhydrocarbons of carbon number range C₅ to about C₄₀ or higher.Preferably, the synthesized hydrocarbons are primarily or almostcompletely paraffins.

The catalyst, cobalt and ruthenium on titania, contains about 5 to 25wt. % cobalt, preferably 10 to 15 wt. % cobalt and about 0.03 to 0.30%ruthenium, preferably about 0.1 to 0.2 wt. % ruthenium. The atomic ratioof cobalt to ruthenium is about 10 to 400, preferably about 100 to 200.

The catalytic metals are supported on titania which may be used alone orwith other inorganic refractory materials. Preferably, the supportmaterial is titania and more preferably the titania has a rutile:anataseratio of at least about 2:3 as determined by x-ray diffraction (ASTMD3720-78), preferably about 2:3 to about 100:1 or higher, morepreferably about 4:1 to 100:1 or higher, e.g., 100% rutile. The surfacearea of the support is, generally, less than about 50 m² /gm (BET).

Preparation of the catalyst is not believed to be a critical stepinsofar as deposition of the catalytic metals on the support isconcerned. The intimate contact between the cobalt and the ruthenium isaccomplished by subjecting the composition to an oxygen treatmentsubsequent to reduction of both of the metals. Consequently, the metalscan be deposited (i.e., impregnated) on the support either in serialfashion--with the cobalt being deposited either before or afterdepositing the ruthenium--or by co-impregnating the metals onto thecarrier. In the case of serial impregnation, the carrier is preferablydried and the metal reduced prior to impregnation of the second metalafter which drying and reduction is effected again and prior to thetreatment of the catalyst with an oxygen containing gas.

Preferably, the catalyst is prepared by depositing the cobalt, dryingthe catalyst, reducing the cobalt, depositing the ruthenium, alsofollowed by drying and reduction, and to effect the intimate contact ofthe cobalt and ruthenium exposure to an oxygen containing gas, and afinal reduction.

Thus, the catalyst can be prepared by incipient wetness impregnation ofthe titania support with an aqueous solution of a cobalt salt, e.g.,nitrate, acetate, acetyl acetonate or the like, the nitrate beingpreferred. The impregnated support is then dried and reduced in areducing gas, such as hydrogen. Ruthenium is added to the reduced cobalton titania catalyst using a ruthenium salt, e.g., ruthenium nitrate,chloride, acetylacetonate, carbonyl, etc. The catalyst is again driedand again reduced in a reducing gas, such as hydrogen. Intimateassociation of the cobalt and ruthenium is accomplished by treating thereduced cobalt-ruthenium on titania catalyst with an oxidizing gas,e.g., air or a dilute oxygen stream such as 20% oxygen in helium atelevated temperatures sufficient to oxidize the cobalt and ruthenium,for example above about 250° C., preferably 250° to 300° C.; but not inexcess of about 600° C. because of excessive oxide sintering. Uponreduction, the cobalt and ruthenium are intimately associated, that is,atoms of each are much closer together than would otherwise be the caseand are believed to be present in the same crystallite. Cobalt andruthenium oxides in the bulk form a cobalt-ruthenium single phase mixedmetal oxide. The available evidence suggests a likely bimetallic clusterformation of Co and Ru on the titania support. Reduction is effected inhydrogen at about 400° C. but can take place at temperatures rangingfrom about 200° to 500° C. Reduction of the catalyst is generallyeasier, that is, occurs at lower temperatures, relative to a catalystcontaining only cobalt without ruthenium.

In virtually any catalytic process, catalyst activity decreases as runlength increases due to a variety of factors: deposition of coke orcarbon on the catalyst as a result of cracking, hydrogenolysis, orpolymerization, buildup of poisons in the feed such as sulfur ornitrogen compounds, etc. In hydrocarbon synthesis reactions carbon tendsto build up or grow (by complex polymerization mechanisms) on thesurface of the catalyst, thereby shielding the catalytic metals from thereactants. Activity decreases and at some pre-set level of activity (asdefined by conversion or selectivity or both), the process becomessufficiently uneconomical to continue and the catalyst is eitherreplaced or regenerated. In either case, downtime results and in theformer, significantly increased catalyst costs are incurred.

Catalyst regeneration is desirable, particularly where regeneration canbe accomplished without removing the catalyst from the reactor. Usingthe catalyst of this invention, regeneration can be effected bydiscontinuing the flow of carbon monoxide (and continuing the flow ofhydrogen if the gases are supplied separately) to the reactor ordiscontinuing the flow of synthesis gas (where synthesis gas is the feedas produced, for example, by methane reforming or partial oxidation ofmethane) and flowing hydrogen to the reactor. After regeneration withhydrogen, synthesis gas flow to the reactor is resumed and thehydrocarbon synthesis reaction continued. The regeneration process maybe conducted at intervals to return the catalyst to initial activitylevels. Thus, a cyclical operation involving hydrocarbon synthesis andregeneration may be repeated.

The temperature in the reaction zone during hydrogen regeneration ispreferably at or slightly above hydrocarbon synthesis reactiontemperatures and pressures can be the same, as well; although neithertemperature nor pressure are critical to the regeneration which iseffected by the hydrogenolysis characteristics of the ruthenium boundintimately with the cobalt. In the case where the ruthenium is notintimately bound with the cobalt, i.e., not in the same crystallite,hydrogenolysis of the carbon deposited on the catalyst may have littleor no effect on carbon deposited on the cobalt sites. Where theruthenium and cobalt are in intimate association, ruthenium-promotedhydrogenolysis affects the carbon deposited on the particularcrystallite and both cobalt and ruthenium sites are regenerated, thatis, freed of carbon deposits. It is only necessary that the conditionsbe conducive to hydrogenolysis promoted by ruthenium and carried out fora time sufficient to regenerate the catalyst. Preferably, temperaturesrange from about 150° C. to about 300° C., more preferably about 190° C.to 260° C. and the hydrogen flow is continued until regeneration iseffected, about 8 hours, preferably at least about 10 hours.

Regeneration results in the recovery of at least about 90%, preferably95%, more preferably at least 100% of initial activity as measured bycobalt-time yields and is accompanied by C₅ + yields greater thaninitially and CH₄ yields below initial yields. By "initial" we meanafter the catalyst has stablized, usually about 24 hours after startup.

EXAMPLE 1: PREPARATION AND EVALUATION OF SUPPORTED COBALT CATALYSTS

Four cobalt-containing catalysts were prepared, three with titania as asupport and one with silica. For catalyst A, 50 grams of Degussa P-25titania was calcined at 560° C. for 4 hours. X-ray diffraction showedthat the titania contained 70% rutile and 30% anatase; the BET-measuredsurface area was 30m² /gm. 35 gms of cobalt nitrate hexahydrateCo(NO₃)2.6H₂ O. (Alfa, Puratronic Grade) were dissolved in 20 cc ofdoubly-distilled deionized water. Half of the solution was impregnatedby incipient wetness onto the titania. After the sample was dried at100° C. the remaining solution was impregnated onto the titania and thecatalyst was dried at 100° for 16 hours. Following calcination in air at400° C. for 4 hours, the catalyst was placed in a tube furnace at 400°C. in a hydrogen flow of 2000 cc H₂ /cc cat/hr for a period of 16 hours.After this reduction, He was introduced for 2 hours and then a 1% streamof oxygen was added to the helium to passivate the catalyst and allowits removal into the ambient environment. Subsequent cobalt chemicalanalysis showed the cobalt content to be 11.6%. Catalyst A thereforeconsists of 11.6% Co/TiO₂ and is designated at Co/TiO₂ in the followingexamples.

For catalyst B, 20 grams of 11.6% Co/TiO₂ (a portion of catalyst A) wereselected. 1.02 grams of ruthenium nitrate (hydrate) were dissolved in102 cc of acetone. 20 grams of catalyst A were slurried into thissolution and the solvent was allowed to evaporate while being stirred.The catalyst was dried, reduced, and passivated as described above.

To prepare Catalyst C, 10 grams of B were heated in 20% O₂ /80% He at300° C. for 4 hrs., rereduced in H₂ and passivated as described above.The cobalt and ruthenium contents in catalysts B and C were 11.6 and0.14% respectively, corresponding to an atomic Co/Ru ratio of 160. Thecatalysts B and C are designated as CoRu/TiO₂ and CoRu(c)TiO₂ in thefollowing examples.

Catalyst D, containing cobalt on silica, was prepared for comparisonpurposes. 30 grams of Davison 62 silica were calcined at 600° C. for 4hours. 50 grams of cobalt nitrate hexahydrate were dissolved in 40 cc ofwater. The solution was impregnated onto the silica in four steps withintermediate dryings at 100° C. The catalyst was then dried, reduced andpassivated as described above. Chemical analyses indicated that the Cocontent was 23%. This catalyst is designated as Co/SiO₂ in the followingexamples.

EXAMPLE 2: EFFECT OF RU PROMOTER AND CALCINATION AT LOW PRESSURES

5-10 cm³ of catalysts A, B, C and D from Example 1 were run in a singlepass fixed bed reactor of ∛ inch outer diameter. Hydrogen, carbonmonoxide and nitrogen were obtained as a preblended mixture with 61±2%H₂, 31±2% CO and 7±1% N₂. The feed mixture was passed over a Pd/Al₂ O₃catalyst (Deoxo, Johnson Mathey), an activated charcoal sieve, and a 13Xmolecular sieve trap, to remove water, oxygen, and Ni and Fe carbonyls.Gas flows were controlled by Brooks mass flow controllers. Pressure wasmaintained with backpressure regulators. Temperature was held isothermalto within ±2 degrees by use of a Thermac temperature controller.Products were analyzed by capillary and packed column gaschromatography, using N₂ as an internal standard. C₂₀ -C₂₀₀ molecularweight distributions were obtained by gas chromatography and gelpermeation chromatography. Pretreated and passivated catalysts wererereduced in flowing hydrogen (200-400 GHSV) at 400° C. for 4 hours inthe hydrocarbon synthesis reactor before Fischer-Tropsch experiments.

Table I compares the Fischer-Tropsch synthesis behavior of Co/TiO₂(Catalyst A) with the bimetallic CoRu/TiO₂ both directly reduced(Catalyst B) and calined/rereduced (Catalyst C) as well as thecomparative Co/SiO₂ catalyst (Catalyst D). Hydrocarbon synthesis ratesare reported as cobalt-normalized rates, i.e., cobalt time-yields,defined as the moles of CO converted per hour per g-atom Co in thecatalyst or as site-normalized rates (site-time yields) defined as themolecules of CO converted per hour per surface cobalt atom in thecatalyst. The number of surface cobalt atoms is determined from H₂chemisorption measurements. Hydrocarbon selectivities are reported on acarbon atom basis as the percentage of the converted CO which appears asa given product.

At 560 kPa the addition of Ru to Co/TiO₂ (Co/Ru gm atom ratio 160)increases time yields more than threefold while decreasing CH₄selectively from 10.1% to 7.9%. Calcination of the bimetallic catalysthas a minor effect on selectivity, but it increases time yields by anaddtional 50%. Co/SiO₂ shows similar selectivities with about 50% highertime yield than Co/TiO₂, because of the proportionately higher cobaltloading.

EXAMPLE 3:

Catalysts A, B, and C were also compared at higher pressure, 2050 kPa,in the same reactor. Table II lists the results. At these conditionscalcination of the bimetallic Co-Ru/TiO₂ significantly improvesperformance. Time yields double with the addition of Ru to the Co/TiO₂but improve an additional 70% following calcination. In addition, CH₄selectivity decreases from 7.5 to 5.0% and the C₅ + fraction increasesfrom 86 to 91% following calcination and reduction.

EXAMPLE 4

Catalysts A, B and C from Example 1 were run in a fixed bed reactor asdescribed in Example 2 at 200° C. and 560 kPa. During the run theconversions were varied between 5 and 70% by adjusting the spacevelocity between 200 and 3000 v/v/hr. Table III shows the CH₄ and C₅ +selectivities as a function of CO conversion. For all three catalysts,the CH₄ selectivity decreases and the C₅ + selectivity increases withincreasing conversion. At all conversion levels the methane yields arelower and C₅ + yields higher for the Ru promoted catalysts. At alllevels of conversion the calcination of the CoRu/TiO₂ catalyst decreasesCH₄ and increases C₅ + selectivities.

                                      TABLE I                                     __________________________________________________________________________    Fischer-Tropsch Activities                                                    and Selectivities at 560 kPa                                                              CO                                                                            Conversion                                                                          CH.sub.4                                                                           CH.sub.5 +                                                                         Cobalt-Time                                                                          Space-Time                                 Catalyst                                                                              GHSV                                                                              %     (% Wt)                                                                             (% Wt)                                                                             Yield (h.sup.-1)                                                                     Yield (h.sup.-1)                           __________________________________________________________________________    Co/SiO.sub.2 (D)                                                                       450                                                                              28.9  8.4  78.8 130    1.0                                        Co/TiO.sub.2 (A)                                                                       300                                                                              27.7  10.1 79.4  83    0.6                                        CoRu/TiO.sub.2 (B)                                                                    1200                                                                              26.0  7.9  85.7 310    2.0                                        CoRu/TiO.sub.2 (C)                                                                    1800                                                                              25.3  7.5  86.7 455    2.9                                        (Calcined)                                                                    __________________________________________________________________________     [200° C., H.sub.2 /CO = 2.05, 560 kPa]-                           

                                      TABLE II                                    __________________________________________________________________________    Fischer-Tropsch Activities                                                    and Selectivities at 2050 kPa                                                             CO                                                                            Conversion                                                                          CH.sub.4                                                                           CH.sub.5 +                                                                         Cobalt-Time                                                                          Space-Time                                 Catalyst                                                                              GHSV                                                                              %     (% Wt)                                                                             (% Wt)                                                                             Yield (h.sup.-1)                                                                     Yield (h.sup.-1)                           __________________________________________________________________________    Co/TiO.sub.2 (A)                                                                      450 48.7  7.0  85.0 220    1.4                                        CoRu/TiO.sub.2 (B)                                                                    800 50.7  7.5  86.1 405    2.6                                        CoRu/TiO.sub.2 (C)                                                                    1200                                                                              61.0  5.0  91.4 730    4.7                                        (Calcined)                                                                    __________________________________________________________________________     [200° C., H.sub.2 /CO = 2.05, 2050 kPa]-                          

                                      TABLE III                                   __________________________________________________________________________    Fischer-Tropsch Activities and Selectivities as a Function of Conversion      Catalyst  Co/SiO.sub.2 (D)                                                                     Co/TiO.sub.2 (A)                                                                     CoRu/TiO.sub.2 (B)                                                                    CoRu(c)/TiO.sub.2 (C)                         __________________________________________________________________________    Cobalt Time Yield                                                                       1  1   0.6                                                                              0.6 2.0 2.0 2.9  2.8                                      CO Conversion                                                                           7  65  4  50  5   64  5    68                                       CH.sub.4 Selectivity                                                                    9.5                                                                              7.4 12 9.3 8.6 6.8 7.8  6.5                                      C.sub.5 + Selectivity                                                                   75 82  77.3                                                                             80.2                                                                              84.9                                                                              87.3                                                                              85.3 87.8                                     __________________________________________________________________________     Conditions: 200° C., 560 kPa, H.sub.2 /CO = 2/1, conversion varied     by changing space velocity                                               

EXAMPLE 5

Catalysts A, B and C from Example 1 were run for periods of 10-30 days.During those time periods catalyst activity declines. Table IV shows theeffect of hydrogen treatments on reactivating these catalysts.

                  TABLE IV                                                        ______________________________________                                        Regeneration of Co                                                            Catalysts by H.sub.2 Treatments                                                               Cobalt-                                                                       Time                                                                          Yield  CH.sub.4 C.sub.5 +                                                     (h.sup.-1)                                                                           (Wt %)   (Wt %)                                        ______________________________________                                        (A)  Co/TiO.sub.2 (4)                                                              Initial          0.6      8.9    80.1                                         Before H.sub.2 treatment (2)                                                                   0.5      9.5    81                                           After H.sub.2 treatment (1)                                                                    0.5      9.5    80.5                                    (B)  CoRu/TiO.sub.2 (3)                                                            Initial          2.6      7.0    86                                           Before H.sub.2 treatment (2)                                                                   2.0      8.2    84                                           After H.sub.2 treatment (1)                                                                    2.6      6.5    87                                      (C)  CoRu/TiO.sub.2 (3) (calcined)                                                 Initial          4.5      5.5    91.0                                         Before H.sub.2 treatment (2)                                                                   3.9      6.4    88.8                                         After H.sub.2 treatment (1)                                                                    4.8      4.9    91.5                                    ______________________________________                                         (1) 24-48 hr. after H.sub.2 -                                                 (2) H.sub.2 treatment at 200-230° C. for 16 hr, 100 kPa                (3) Conditions, 50-60% CO conversion, 2060 kPa, 200° C., H.sub.2       /CO = 2/1                                                                     (4) Conditions, 20% CO conversion 560 kPa, 200.sup.2 C, H.sub.2 /CO = 2/1

For Co/TiO₂, the CO conversion and CH₄ and C₅ + selectivities do notrespond appreciably to H₂ treatments, whereas the Ru containingcatalysts respond to the hydrogen treatment by regaining their originalactivity and selectivity. For the calcined catalyst (C), all results aresuperior to the results for the uncalcined catalyst (B).

EXAMPLE 6

The calcined Co-Ru/TiO₂ catalyst (catalyst C) was run at twotemperatures at a constant pressure of 2060 kPa. Space velocities wereadjusted to keep conversion levels comparable. Table V presents theresults.

                  TABLE V                                                         ______________________________________                                        Effect of Temperature on                                                      Performance of CoRu(c)/TiO.sub.2 (C)                                          ______________________________________                                        Temperatures T/°C.                                                                        184.8   200.0                                              GHSV               600     1200                                               CO Conversion (%)  57.2    59.1                                               Cobalt-Time Yield (h.sup.-1)                                                                     2.2     4.6                                                E.sub.CO /Kcal mol.sup.1                                                                         21                                                         Carbon Selectivity (%)                                                                           3.4     5.4                                                CH.sub.4                                                                      E.sub.CH4 (Kcal mol.sup.-1)                                                                      34                                                         C.sub.2            0.40    0.43                                               C.sub.3            1.59    1.68                                               C.sub.4            1.66    1.77                                               C.sub.5 +          92.9    90.7                                               ______________________________________                                         [CoRu(C)/TiO.sub.2 2060 kPa, H.sub.2 /CO =                                    0.14% Ru, 11.6% Co                                                       

At higher temperatures selectivity to lighter products increases. Thecalcined Ru promoted catalyst run at 15° C. lower temperature has cobalttime yields comparable to the unpromoted Co/TiO₂ and much higher C₅ +selectivity. Therefore, improved selectivities (less CH₄ and more C₅ +)are obtainted at comparable metal yields.

EXAMPLE 7

Catalysts A and C were compared at different temperatures. Table VIlists the results.

                  TABLE VI                                                        ______________________________________                                                  CoRu(C)/TiO.sub.2 (C)                                                                     Co/TiO.sub.2 (A)                                        ______________________________________                                        Temp.       185           200                                                 Co Time     2.2           1.4                                                 Yield (h.sup.-1)                                                              C.sub.5 +   93            85                                                  CH.sub.4    3.4           7                                                   ______________________________________                                    

The data show that at similar cobalt time yields, the CoRu(c)/TiO₂catalyst produces substantially more C₅ + and less CH₄ than the Co/TiO₂catalyst, the calcined catalyst being more active and more selective tovaluable products.

EXAMPLE 8

The Co/TiO₂ and CoRu(c)/TiO₂ catalysts from Example 1 were treated underhydrogen in a thermalgravimetric analyzer (TGA). The samples were heatedfrom room temperature to 500° C. at 6 deg/min. The TG curve monitorsweight changes as the cobalt oxide is reduced to cobalt metal. The DTGplots the rate of weight change with time as a function of temperture.FIG. 1 shows the onset of reduction begins at a lower temperature withthe CoRu(c)/TiO₂ catalyst. This indicates that the cobalt and rutheniumhave come into intimate association on the catalyst. FIG. 2 shows thebehavior of the Co/TiO₂ and CoRu(c)/TiO₂ catalysts in a 1:1 H₂ /COmixture following reduction. The calcined CoRu/TiO₂ catalyst does notgrow carbon at temperatures where the noncalcined CoRu/TiO₂ or Co/TiO₂do. Therefore, a combination of increased cobalt oxide reducibility andinhibited catalyst poisoning by carbon are believed to account for theincreased number of active sites observed on calcined CoRu/TiO₂catalysts.

EXAMPLE 9

CoRu/TiO₂ (catalyst B) and CoRu(c)/TiO₂ (catalyst C) were run underFischer-Tropsch conditions for 700 hours, including two hydrogenregeneration treatments.

Electron microscopy studies of these catalysts were conducted using aPhillips EM-420ST high-resolution transmission electron microscope withscanning transmission and energy dispersive x-ray analysis capabilities.Under the conditions used in this study, the instrument had a resolutionof better than 0.25 nm. The catalyst samples were ground using a mullitemortar and pestle and was ultrasonically dispersed in butyl alcohol. Adrop of the suspension was then air dried on a carbon film.

Identification of the elements in the catalyst was made using theadjunct energy dispersive x-ray (EDX) analyzer. Using the EDX system,particles as small as 1 nm were analyzed. With these catalysts and witha 1 nm beam for analysis, the x-ray spatial resolution was approximately2.5 nm. Detectability limits for the elements in question were about0.3-0.4 weight percent in the volume analyzed. FIG. 3 shows the results.

The morphology of the cobalt particles on titania is similar on bothmonometallic and bimetallic catalysts. Cobalt is dispersed on thetitania as slightly elliptical particles 20-50 nm in size. EDX analysisof these particles suggests that ruthenium is present with the cobalt inthe same crystallite after calcination and reduction treatments. FIG. 3shows that following the calcination and rereduction treatment theruthenium has concentrated in the area of the cobalt particles so thatruthenium above detectability limits was not observed on the titania,but was only in the cobalt particles. (In the uncalcined CoRu/TiO₂ (FIG.4), ruthenium was below detection limits on the support and in thecobalt particles, indicating that Ru was not preferentiallyconcentrated, but remained uniformly present.)

What is claimed is:
 1. A hydrocarbon synthesis process which comprisesreacting hydrogen and carbon monoxide in the presence of a catalystcomprised of cobalt and ruthenium on titania, at reaction conditionssuitable for the formation of higher hydrocarbons, the catalyst beingprepared by impregnating titania with solutions of cobalt and rutheniumsalts, drying the impregnated support, reducing the cobalt andruthenium, treating the reduced metals with an oxygen containing streamat conditions sufficient to form oxides of cobalt and oxides ofruthenium and reducing the cobalt and ruthenium oxides.
 2. The processof claim 1 wherein the ratio of hydrogen to carbon monoxide in thesynthesis gas is about 0.5 to 4.0 and reaction temperatures range fromabout 160° C. to about 300° C.
 3. The process of claim 1 wherein thehydrocarbon synthesis process is intermittently interrupted, feed to thecatalyst is discontinued and the catalyst is regenerated in the presenceof hydrogen.
 4. The process of claim 3 wherein regeneration is effectedat temperatures ranging from about 160° C. to about 300° C. and at leastabout 90% of the catalyst's initial activity is recovered.